How many molecules are in 120 g of CO2?

Iam in desperate need of with this !

What mass of natural gas (ch4) must you burn to emit 276 kj of heat?

Two metal blocks that have slightly different temperatures are placed next to one another. after five minutes, they both have lower but equal temperatures. according to the law of conservation of energy, what  most likelyhappened? energy was created inside the blocks.energy was destroyed inside the blocks.energy was absorbed into the blocks from outside the system.energy was transferred from the warmer block to the cooler block.